1. FIELD OF THE INVENTION
This invention relates in general to orifice plate equipment for measuring fluid flow in pipelines, and in particular to a valve seal strip for sealing between the lower chamber and the upper chamber of an orifice fitting.
2. DESCRIPTION OF THE PRIOR ART
One method of measuring fluid flow in pipelines is by the use of an orifice fitting. An orifice fitting is an assembly that will be mounted to a pipeline for receiving fluid flow. It has a body with a passage for the flow of the fluid. The body has an upper chamber and a lower chamber separated by a slot. A gear mechanism will lower an orifice plate from the upper chamber, through the lower chamber and down into the fluid flow passage. The orifice plate has a hole through it. Fluid flow through the hole causes a pressure drop. The difference in pressure upstream and downstream of the plate corresponds to the volume of fluid flow.
While the orifice plate is in an inactive position in the upper chamber, and also while the orifice plate is in the active position in the flow passage, the slot between the upper and lower chambers must be sealed. This is handled by a slide valve carrier. The slide valve carrier has a metal seal strip mounted on its upper side. A gear mechanism will move the slide valve laterally, causing the seal strip to seal against the seat surrounding the slot. Springs urge the seal strip upward against the seat.
Grease injection passages extend from the upper chamber down through the seat. A groove surrounds the slot and communicates with the grease injection passages. A fitting will allow the introduction of grease to the groove around the slot to enhance sealing of the valve seal strip.
While this is workable, tolerances on the assembly are high. If moved too far in one direction, the seal strip may be misaligned with the grease injection grooves. This could expose pressure in the lower chamber to the grease injection fitting.